Scientists discover why birds fly in a V

Birds of a feather may flock together, but why they fly together in V formations has never been known for certain. Now, with the help of 14 northern bald ibises fitted with lightweight sensors on a 1000-kilometre migration from Austria to Tuscany, researchers are suggesting that the explanation is one that was long suspected but never proved: the formation helps the birds conserve energy.

Reporting in the journal Nature, the scientists write that the ibises positioned themselves in spots which were aerodynamically optimal, allowing them to take advantage of swirls of upward-moving air generated by the wings of the bird ahead. The lead bird gets no lift advantage; the ibises regularly switched leaders.

''We've been wondering for years whether flapping birds can save energy by following each other in the right way,'' said Geoffrey Spedding, chairman of the aerospace and mechanical engineering department at the University of Southern California, who was not involved in the study. ''This work answers that question, and the answer is yes.''

The study looked at ibises, but experts say it could apply to other birds that fly in V formations as well, such as ducks and pelicans.

Training flight: The ibises followed behind researchers in a paraplane. Photo: AP

The scientists, led by Jim Usherwood of the Royal Veterinary College in Britain, said a major challenge was obtaining the data. The ibises were hatched at Zoo Vienna in March 2011 and raised as part of a project aimed at reintroducing the endangered species to its natural range in Europe.

Some of the study's authors served as human foster parents, taking the young birds on training flights. The humans rode in a paraplane, a lightweight aircraft attached to a parachute, and the birds followed.

An analysis of 24,000 flaps showed that the ibises on average adjusted their position to optimise the lift from the vortices, and readjusted their phasing when they changed positions within the V. The study does not say how much energy was saved, but small gains could be useful over long migrations, experts say.

Another question is how the birds know to fly in these optimal spots. Dr Usherwood said that they might have evolved ''rules of thumb'', or that ''they have good sensors'' and adjust to find spots that feel good. ''Splitting apart those possibilities would be possible with cunning experiments we have planned,'' he said.